Hybridization traditionally is understood as the process which, under predetermined reaction conditions, two partially or completely complimentary strands of deoxyribonucleic acid molecules (DNA), ribonucleic acid molecules (RNA), and combinations of DNA and RNA, are separated into single strands and then allowed to anneal forming base-paired double helices. The term in situ hybridization, as used herein, refers to a hybridization technique which effectively detects specific nucleic acid sequences in intact cells or tissues. The technique of in situ hybridization provides the added benefit of also yielding morphological information about the individual intact cells.
In situ hybridization technique was first described by Gall and Padre (Proc. Nat. Acad Sciences 63: 378-83 (1969)) and Jone et al. (Nature 225: 946-8 (1969)). Both groups looked at formation and detection of RNA-DNA hybrids in cytological preparations using radiolabeled probes. The technique permits detection of DNA or RNA in individual cells which contain specific sequences, in a heterogeneous cell population. It also allows the simultaneous determination of biochemical and morphological characteristics of the examined cells. Since its initial description, in situ hybridization has undergone continuous evolution in methodology and application. At present the technique has direct applications in many areas of biomedical and clinical research including cell biology, clinical diagnosis, developmental biology, genetics and virology.